This invention relates to axial split-pin tumbler-type lock mechanisms having structure designed to render them resistant to picking.
In general, the axial split-pin tumbler-type lock mechanisms include a rotatable operating part and a stationary part, which adjoin at an interfacial plane. Tumblers each including a driver element and a follower element are mounted in bores in the parts, which bores meet in alignment at the interfacial plane, and the tumblers are movable back and forth in the bores. When the joints between the tumbler elements coincide with the interfacial plane upon insertion of the proper key, the operating part may be rotated by means of the key, to accomplish a desired function. Illustrative of the lock mechanisms to which the present invention is directed are Kerr U.S. Pat. No. 3,541,819, Kerr U.S. Pat. No. 3,813,906, and Steinbach U.S. Pat. No. 3,916,657.
As disclosed in U.S. Pat. No. 3,541,819, the lock mechanisms of the foregoing type have in the past been picked, employing what may be referred to as a "gang pick", of the type disclosed in the patent. In use, the pick is applied to the lock mechanism, a rotational torque or bias is applied to the operating part thereby, to displace the operating part to a slight extent relative to the stationary part, and a jiggling motion is utilized to catch tumbler elements on the margins of tumbler bores which project over adjacent bores, until elements of all of the tumblers have been caught at the interfacial plane in such manner and the operating part is free to rotate, the mechanism then being in unlocked condition. Numerous improvements have been devised to increase the pick resistance of such lock mechanisms, as illustrated by the foregoing patents, and they have met with varying degrees of success.